如何获取实时数据库中的特定密钥？

debugcn 发表于 Dev

凯

我目前无法从Firebase删除特定数据。所以基本上我有recyclerview，其中显示了我的数据，并且每个数据显示中都有一个按钮，这是“编辑”按钮。每当我尝试单击“编辑”按钮时，它都应该让我进行另一个活动，并在recyclerview中显示相同的数据，并且在那里显示另一个按钮，即“删除”按钮。但是，每当我尝试单击删除按钮时，它都会从子级中删除所有数据。我仅需要删除发生意图时传递的选定ID /数据。编辑。

EditResearch.java

package com.example.citeresearchrepository.AdminPackage;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.OnProgressListener;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.UploadTask;

public class EditResearchActivity extends AppCompatActivity {
    EditText editfilehandler_et,editrepo_title,editrepo_description,editrepo_currentdate;
    Button editrepo_savebtn;
    ImageView backbtn_editresearch;
    DatabaseReference databaseReference;
    FirebaseDatabase firebaseDatabase;
    StorageReference storageReference;
    String researchtitle,researchdate,researchname,researchdescription;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_edit_research);
        editfilehandler_et = findViewById(R.id.editfilehandler_et);
        editrepo_title = findViewById(R.id.editrepo_title);
        editrepo_description = findViewById(R.id.editrepo_description);
        editrepo_currentdate = findViewById(R.id.editrepo_currentdate);

        editrepo_savebtn = findViewById(R.id.editrepo_savebtn);
        backbtn_editresearch = findViewById(R.id.backbtn_editresearch);
        Intent intent = getIntent();
        researchtitle = intent.getStringExtra("researchtitle");
        researchdate = intent.getStringExtra("researchdate");
        researchname = intent.getStringExtra("researchname");
        researchdescription = intent.getStringExtra("researchdescription");

        databaseReference = FirebaseDatabase.getInstance().getReference("ResearchRepository");
        storageReference = FirebaseStorage.getInstance().getReference();
        editfilehandler_et.setText(researchname);
        editrepo_title.setText(researchtitle);
        editrepo_currentdate.setText(researchdate);
        editrepo_description.setText(researchdescription);

        editrepo_savebtn.setEnabled(false);
        editfilehandler_et.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                selectPDF();
            }
        });
        /* Update Files */

        backbtn_editresearch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(getApplicationContext(), AdminResearchRepoActivity.class));
            }
        });

    }
    private void selectPDF(){
        Intent intent = new Intent();
        intent.setType("application/pdf");
        intent.setAction(intent.ACTION_GET_CONTENT);
        startActivityForResult(Intent.createChooser(intent, "PDF FILE SELECTED"), 12);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable final Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(requestCode==12 && resultCode == RESULT_OK && data!=null && data.getData()!=null){
            editrepo_savebtn.setEnabled(true);
            editfilehandler_et.setText(data.getDataString().substring(data.getDataString().lastIndexOf("/") + 1));
            editrepo_savebtn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    deletePreviousImage();
                    uploadResearch(data.getData());
                }
            });
        }
    }
    private void deleteSelectedRow(){
        firebaseDatabase = FirebaseDatabase.getInstance();
        databaseReference = firebaseDatabase.getReference("ResearchRepository");
        databaseReference.removeValue();
    }
    private void uploadResearch(Uri data) {
        final String filecapture = editfilehandler_et.getText().toString();
        final String researchtitle = editrepo_title.getText().toString();
        final String researchdescription = editrepo_description.getText().toString();
        final String researchtimeline = editrepo_currentdate.getText().toString();
        final ProgressDialog progressDialog = new ProgressDialog(this);
        progressDialog.setTitle("File Uploading...");
        progressDialog.show();

        StorageReference reference = storageReference.child("ResearchRepository" +System.currentTimeMillis() + ".pdf");

        reference.putFile(data).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
            @Override
            public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
                Task<Uri> uriTask = taskSnapshot.getStorage().getDownloadUrl();
                while(!uriTask.isComplete());
                Uri uri = uriTask.getResult();

                ResearchRepository researchRepository = new ResearchRepository(filecapture,researchtitle,researchdescription,researchtimeline,uri.toString());
                databaseReference.child(databaseReference.push().getKey()).setValue(researchRepository);
                Toast.makeText(EditResearchActivity.this, "File Uploaded", Toast.LENGTH_SHORT).show();
                progressDialog.dismiss();
                editfilehandler_et.setText("");
                editrepo_title.setText("");
                editrepo_currentdate.setText("");
                editrepo_description.setText("");
                startActivity(new Intent(getApplicationContext(), AdminResearchRepoActivity.class));

            }
        }).addOnProgressListener(new OnProgressListener<UploadTask.TaskSnapshot>() {
            @Override
            public void onProgress(@NonNull UploadTask.TaskSnapshot snapshot) {
                double progress = (100*snapshot.getBytesTransferred())/snapshot.getTotalByteCount();
                progressDialog.setMessage("File Uploading..."+(int)progress+"%");
            }
        });
    }
    private void deletePreviousImage(){
        StorageReference reference = FirebaseStorage.getInstance().getReference().child(researchtitle);
        reference.delete().addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {
                Toast.makeText(EditResearchActivity.this, "Previous File Deleted", Toast.LENGTH_SHORT).show();
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(EditResearchActivity.this, e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }

}

AdminResearchRepoActivity.java

package com.example.citeresearchrepository.AdminPackage;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.Toast;

import com.example.citeresearchrepository.AdminAdapter.AdminRepoAdapter;
import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;
import com.example.citeresearchrepository.ViewHolder.AdminResearchRepositoryViewHolder;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;

public class AdminResearchRepoActivity extends AppCompatActivity {
    ImageView adminrepo_backbtn;
    RecyclerView reporecycler;
    FloatingActionButton addresearch_btn;

    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    AdminRepoAdapter adminRepoAdapter;
    ArrayList<ResearchRepository> researchRepositoryArrayList = new ArrayList<>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_research_repo);

//      Buttons
        adminrepo_backbtn = findViewById(R.id.backbtn_adminrepo);
        addresearch_btn = findViewById(R.id.addresearch_btn);

        addresearch_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(getApplicationContext(), AddResearchActivity.class));
            }
        });
        adminrepo_backbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(getApplicationContext(), WelcomeAdminActivity.class));
            }
        });

//      Recycler
        reporecycler = findViewById(R.id.reporecycler);
        reporecycler.setLayoutManager(new LinearLayoutManager(this));

//      Firebase Connection
        firebaseDatabase = FirebaseDatabase.getInstance();
        databaseReference = FirebaseDatabase.getInstance().getReference().child("ResearchRepository");
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                researchRepositoryArrayList = new ArrayList<ResearchRepository>();
                for (DataSnapshot dataSnapshot: snapshot.getChildren()){
                    ResearchRepository researchRepository = dataSnapshot.getValue(ResearchRepository.class);
                    researchRepositoryArrayList.add(researchRepository);
                }
                adminRepoAdapter = new AdminRepoAdapter(AdminResearchRepoActivity.this,researchRepositoryArrayList);
                reporecycler.setAdapter(adminRepoAdapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(AdminResearchRepoActivity.this, error.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });

    }

}

AdminRepoAdapter.java

package com.example.citeresearchrepository.AdminAdapter;

import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.citeresearchrepository.AdminPackage.EditResearchActivity;
import com.example.citeresearchrepository.Model.ResearchRepository;
import com.example.citeresearchrepository.R;

import java.lang.reflect.Array;
import java.util.ArrayList;

public class AdminRepoAdapter extends RecyclerView.Adapter<AdminRepoAdapter.AdminViewHolder>  {

    Context context;
    ArrayList<ResearchRepository> researchRepositories;

    public AdminRepoAdapter(Context c, ArrayList<ResearchRepository> repositories){
        context = c;
        researchRepositories = repositories;
    }

    @NonNull
    @Override
    public AdminViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new AdminViewHolder(LayoutInflater.from(context).inflate(R.layout.admineditrepo_row,parent,false));
    }

    @Override
    public void onBindViewHolder(@NonNull AdminViewHolder holder, final int position) {
        holder.researchtitle_view.setText(researchRepositories.get(position).getResearchtitle());
        holder.researchdate_view.setText(researchRepositories.get(position).getResearchtimeline());
        holder.researchname_view.setText(researchRepositories.get(position).getFilecapture());
        holder.researchdescription_view.setText(researchRepositories.get(position).getResearchdescription());
        holder.btnpdf_edit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(context, EditResearchActivity.class);
                intent.putExtra("researchtitle",researchRepositories.get(position).getResearchtitle());
                intent.putExtra("researchdate",researchRepositories.get(position).getResearchtimeline());
                intent.putExtra("researchname",researchRepositories.get(position).getFilecapture());
                intent.putExtra("researchdescription",researchRepositories.get(position).getResearchdescription());
                v.getContext().startActivity(intent);
            }
        });
    }

    @Override
    public int getItemCount() {
        return researchRepositories.size();
    }

    class AdminViewHolder extends RecyclerView.ViewHolder{
        public TextView researchtitle_view,researchdate_view,researchname_view,researchdescription_view,researchtitle_url;
        public Button btnpdf_edit;

        public AdminViewHolder (@NonNull View itemView) {
            super(itemView);

            researchtitle_view = itemView.findViewById(R.id.researchtitle_view);
            researchdate_view = itemView.findViewById(R.id.researchdate_view);
            researchname_view = itemView.findViewById(R.id.researchname_view);
            researchdescription_view = itemView.findViewById(R.id.researchdescription_view);
            researchtitle_url = itemView.findViewById(R.id.researchtitle_view);
            btnpdf_edit = itemView.findViewById(R.id.btnpdf_edit);
        }
    }
}

ResearchRepository.class

package com.example.citeresearchrepository.Model;

public class ResearchRepository {

    public String filecapture;
    public String researchtitle;
    public String researchdescription;
    public String researchtimeline;
    public String url;

    public ResearchRepository() {
    }

    public ResearchRepository(String filecapture, String researchtitle, String researchdescription, String researchtimeline, String url) {
        this.filecapture = filecapture;
        this.researchtitle = researchtitle;
        this.researchdescription = researchdescription;
        this.researchtimeline = researchtimeline;
        this.url = url;
    }

    public String getFilecapture() {
        return filecapture;
    }

    public void setFilecapture(String filecapture) {
        this.filecapture = filecapture;
    }

    public String getResearchtitle() {
        return researchtitle;
    }

    public void setResearchtitle(String researchtitle) {
        this.researchtitle = researchtitle;
    }

    public String getResearchdescription() {
        return researchdescription;
    }

    public void setResearchdescription(String researchdescription) {
        this.researchdescription = researchdescription;
    }

    public String getResearchtimeline() {
        return researchtimeline;
    }

    public void setResearchtimeline(String researchtimeline) {
        this.researchtimeline = researchtimeline;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }
}

这是我的实时数据库：https : //i.stack.imgur.com/lML0i.png我只想删除红色框。

拉贾·谢卡（Raja Shekar）

从我的角度来看，您正在将实例仅添加到ResearchRepository节点，而不是要删除的特定子节点。您需要跟踪要推送到ResearchRepository节点的唯一ID，并同样将其传递给Intent。

添加代码以传递要删除的ResearchRepository子级的唯一ID。然后在存在删除代码的新活动中执行此操作。

String childToDelete; //retrieve the value from the intent
DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("ResearchRepository").child(childToDelete);
databaseReference.removeValue();

如果那是您的目的，应该这样做。

编辑1：-我明白你的意思。请按照我现在将要显示的方法进行操作，它将为您服务。

如下所示编辑您的课程：-

AdminRepoAdapter.java

public class AdminRepoAdapter extends RecyclerView.Adapter<AdminRepoAdapter.AdminViewHolder>  {

    Context context;
    Map<String,ResearchRepository> researchRepositories;
    ArrayList<ResearchRepository> researchRepositoriesHolder;

    public AdminRepoAdapter(Context c, Map<String,ResearchRepository> repositories){
        context = c;
        researchRepositories = repositories;
        researchRepositoriesHolder = new ArrayList<>(researchRepositories.values());
    }

    @NonNull
    @Override
    public AdminViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new AdminViewHolder(LayoutInflater.from(context).inflate(R.layout.admineditrepo_row,parent,false));
    }

    @Override
    public void onBindViewHolder(@NonNull AdminViewHolder holder, final int position) {
        holder.researchtitle_view.setText(researchRepositoriesHolder.get(position).getResearchtitle());
        holder.researchdate_view.setText(researchRepositoriesHolder.get(position).getResearchtimeline());
        holder.researchname_view.setText(researchRepositoriesHOlder.get(position).getFilecapture());
        holder.researchdescription_view.setText(researchRepositoriesHolder.get(position).getResearchdescription());
        holder.btnpdf_edit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Map.Entry<String,ResearchRepository> entry = null; //Just for initialization
                for (Map.Entry<String,ResearchRepository> var : researchRepositories.entrySet()) {
                    if(var.getValue() == researchRepositoriesHolder.get(position)){
                       entry = var;
                       break;
                    }
                }

                Intent intent = new Intent(context, EditResearchActivity.class);
                intent.putExtra("researchtitle",entry.getValue().getResearchtitle());
                intent.putExtra("researchdate",entry.getValue().getResearchtimeline());
                intent.putExtra("researchname",entry.getValue().getFilecapture());
                intent.putExtra("researchdescription",entry.getValue().getResearchdescription());
                intent.putExtra("childNodeKey",entry.getKey());
                v.getContext().startActivity(intent);
            }
        });
    }

    @Override
    public int getItemCount() {
        return researchRepositoriesHolder.size();
    }

    class AdminViewHolder extends RecyclerView.ViewHolder{
        public TextView researchtitle_view,researchdate_view,researchname_view,researchdescription_view,researchtitle_url;
        public Button btnpdf_edit;

        public AdminViewHolder (@NonNull View itemView) {
            super(itemView);

            researchtitle_view = itemView.findViewById(R.id.researchtitle_view);
            researchdate_view = itemView.findViewById(R.id.researchdate_view);
            researchname_view = itemView.findViewById(R.id.researchname_view);
            researchdescription_view = itemView.findViewById(R.id.researchdescription_view);
            researchtitle_url = itemView.findViewById(R.id.researchtitle_view);
            btnpdf_edit = itemView.findViewById(R.id.btnpdf_edit);
        }
    }
}

AdminResearchRepoActivity.java

public class AdminResearchRepoActivity extends AppCompatActivity {
    ImageView adminrepo_backbtn;
    RecyclerView reporecycler;
    FloatingActionButton addresearch_btn;

    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    AdminRepoAdapter adminRepoAdapter;
    Map<String, ResearchRepository> researchRepositoryMap;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin_research_repo);

//      Buttons
        adminrepo_backbtn = findViewById(R.id.backbtn_adminrepo);
        addresearch_btn = findViewById(R.id.addresearch_btn);

        addresearch_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(getApplicationContext(), AddResearchActivity.class));
            }
        });
        adminrepo_backbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(getApplicationContext(), WelcomeAdminActivity.class));
            }
        });

//      Recycler
        reporecycler = findViewById(R.id.reporecycler);
        reporecycler.setLayoutManager(new LinearLayoutManager(this));

//      Firebase Connection
        firebaseDatabase = FirebaseDatabase.getInstance();
        databaseReference = FirebaseDatabase.getInstance().getReference().child("ResearchRepository");
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                researchRepositoryMap = (Map)snapshot.getValue()
                adminRepoAdapter = new AdminRepoAdapter(AdminResearchRepoActivity.this,researchRepositoryMap);
                reporecycler.setAdapter(adminRepoAdapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(AdminResearchRepoActivity.this, error.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });

    }

}

这样，当您从AdminRepoAdapter将Intent传递给EditResearchActivity时，您的密钥将存储为'childNodeKey'。然后，您可以按照我在编辑之前提到的步骤，使用从此处获得的密钥进行删除。

本文收集自互联网，转载请注明来源。

如有侵权，请联系[email protected] 删除。

编辑于2021-04-5

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